The present invention relates to collapsable elongated articles, and more particularly to collapsable sailboards and surfboards.
Surfboards and recently sailboards have enjoyed considerable market success as recreational vehicles. Sailboards and surfboards are commonly characterized by a single long and relatively narrow hull. A surfboard is propelled by the force produced by breaking waves, while a sailboard is propelled by the force of the wind acting on a sail. The hull must be rigid, as the occupant operates the vehicle while balancing in a standing position. Hence, the hull of these vehicles is most frequently of unitary construction, either of wood in the older models or of a composite structure in the recent models. Commonly, the composite hull will have a central core of relatively soft and/or light material such as balsa wood or foamed plastic, and a laminated outerskin made of plastic or fiberglass. U.S. Pat. No. 4,255,221, issued Mar. 10, 1981 to Young, only one of many techniques for manufacturing a composite hull. One type of sailboard is described in U.S. Pat. No. Re. 31,167, reissued Mar. 8, 1983 to Schweitzer et al.
Sailboard and surfboard hulls are quite bulky, however, rendering them portable only at the expense of special transportation structures. The difficulty of transportation has stimulated development of collapsable structures, generally of either the folding inflatable type or the sectionalized type.
An inflatable structure is disclosed in U.S. Pat. No. 3,577,576, issued May 4, 1971 to Lobb et al. The hull of this collapsable vessel is formed of a flexible sheet material such as polyvinyl chloride, and includes inflatable water tight compartments which are interconnected by channels provided to receive and retain rigid reinforcing elements. The reinforcing elements extend lengthwise through the hull and are interconnected by crossmembers. Another approach is exemplified by U.S. Pat. No. 3,657,753, issued Apr. 25, 1972 to LeBlanc. LeBlanc's collapsable structure comprises an elongated inflatable body having a flexible but substantially non-elastic and transversely convex wall, and an elongated panel adapted to be bowed and hence flexible through its width while, it is said, being longitudinally stiff. The panel overlies the top wall of the inflated body and is maintained in a correspondingly transversely bowed condition. The panel and body are capable of being longitudinaly rolled to reduce their bulk. Yet another approach is exemplified by U.S. Pat. No. 4,253,209, issued Mar. 3, 1981 to Carn. The collapsable sailboard of the Carn patent comprises one or more inflatable bladders and an envelope subdivided into plural demountable longitudinal sections. Rigifying elements cooperate with the bladders and envelope to form a demountable assembly said to resist longitudinal stress.
Unfortunately, the inflatable type of collapsable hull has not been entirely satisfactory in pratice. The reasons are legion. Inflation and deflation of such hulls tends to be time consuming, and may require a separate foot pump and repair kit. The performance of some models tends to be disappointing, either because the hull is not rigid enough for advanced techniques, or because the craft is subject to excessive wind resistence, is relatively unstable because of an elevated center of gravity, or lacks sharp edges or chine, or because inadequate or unequal pressure in one or more compartments as might be brought about by changes in ambient air or water temperature adversely effect the handling quality. Many fabrics suitable for such hulls require great care in storage and handling, and some are subject to ultraviolet and oxygen degredation. Moreover, a puncture of the inflatable structure may result in loss of bouyancy in some models. The use of a platform in some models for attaching the mast and rudder increases the complexity and weight of the hull, and introduces wear problems between fabric and platform and possibly a risk of damage due to rigid sharp structures. Moreover, the manufacturing process is expensive and variations in hull design are severly limited. In addition, some prospective purchasers might consider the inflatable type of collapsable hull to be aesthetically unpleasant.
The sectionalized hull is an alternative to the inflatable collapsable hull. U.S. Pat. No. 3,137,873 issued June 23, 1964 to Garrolini discloses a type of sectionalized hull in whch the adjoining ends of the sectionalized pieces are formed at an angle slightly offset from the perpendicular. The separable body portions are maintained in their assembled condition by means of a pair of telescoping shafts and suitable latches. In the sectionalized hull disclosed in U.S. Pat. No. 3,287,754, issued Nov 9, 1966 to Price et al., the hull sections are maintained together by pairs of laterally spaced clamp assemblies disposed on the upper and lower sides of their respective sections. Longitudinal alignment and assembly of the sections is aided by respective index pins and sockets formed in adjoining edges. U.S. Pat. No. 3,996,868, issued Dec. 4, 1976 to Schagen discloses the the use of tensioning cables extending inside of two horizontally spaced longitudinal spine tubes for retaining the sections together in operation. The tubes are joined by means of connecting sleeves at the juncture of the hull sections. Yet another approach is disclosed in U.S. Pat. No. 3,409,920, issued Nov. 12, 1968 to Brownley. In the sectionalized hull of the Brownley patent, a tapered mortise-and-tenon socket and clip arrangement is used for joining the hull sections. According to the more recently disclosure of a tandem surfer in U.S. Pat. No. 4,100,870, issued July 18, 1978 to Prade, each board of the tandem surfer includes at its coupling edge a stepped zone, which is used for reception and alignment of the individual boards to an intervening coupling member. The intervening coupling member has a mating stepped zone.
Unfortunately, the sectionalized type of collapsable hull have not been entirely satisfactory. The pin-socket type, in particular, suffers a number of disadvantages. Alignment of the sections in practice is sometimes a tedious process. The pin-socket tolerances are somewhat critical for good joint alignment. Yet the pins and sockets are subject to such problems as sand contamination, a particularly troublesome problem with respect to the socket; corrosion in some models; knicking or denting which may prevent assembly; wear in the pin and socket which permits the joint to flex; and adhesion of the dowel pins in the sockets during disassembly. A high clamping force is necessary to maintain joint integrity. In operation, the region in which the dowel pin and sockets are located suffer a concentration of stress, and dowel pin and socket themselves will suffer undue stress as the joint wears. Moreover, a flexing joint may injure the operator. During transportation, the dowel pins protrude on some models, creating a safety hazard and rendering themselves subject to damage. The use of dowel pins increases the manufacturing time and complexity.
Joining techniques have been developed for other purposes as well. The technique disclosed in U.S. Pat. No. 3, 879,782, issued Apr. 29, 1975 to Oliver was developed to couple a removable tail portion to a surfboard. The tail of the surfboard is cut out in a V-shape and provided with a grooved slot. A removable tail portion includes a flange for removably mating with the periphery of the cutout portion. The tail portion is locked to the body of the surfboard with a removable pin.